Wheel loader and method for controlling wheel loader

ABSTRACT

A wheel loader includes: a front frame; a bucket; a boom having a distal end connected to bucket, and a proximal end rotatably supported by front frame; a sensor configured to measure a distance between boom and a loading target; and a controller configured to control an action of wheel loader. The controller causes wheel loader to perform a predetermined action for collision avoidance on condition that a distance to be measured by sensor when wheel loader travels takes a value less than or equal to a threshold value.

TECHNICAL FIELD

The present invention relates to a wheel loader and a method forcontrolling the wheel loader.

BACKGROUND ART

A wheel loader that is an example of self-propelled work vehiclesincludes a traveling apparatus that causes the vehicle to travel, and awork implement that performs various operations/services includingexcavation. The traveling apparatus and the work implement are eachdriven by driving force from an engine.

Japanese Patent Laying-Open No. 2008-303574 (PTL 1) discloses a wheelloader including a video camera or a laser distance sensor disposed on afront wheel axle case. The video camera is configured to capture animage of a road surface forward of a position of a bucket, through aclearance below the bucket. The wheel loader also includes a displayapparatus configured to display an image captured by the video camera ora distance measured by the laser distance sensor on a place where anoperator on an operator's seat sees the image or the distance. Theoperator thus monitors a status of a road surface below a workimplement.

Japanese Patent Laying-Open No. 10-88625 (PTL 2) discloses an automaticexcavator (e.g., a wheel loader) including a visual sensor constitutedof two cameras. In the automatic excavator, the visual sensor measures adistance from the automatic excavator to a target to be excavated or adump truck, for the sake of automatic excavation.

An operator of a wheel loader simultaneously actuates an acceleratorpedal and a boom lever to load, on a bed of a dump truck, soil scoopedby a bucket of a work implement. The wheel loader thus simultaneouslyperforms fore traveling and boom-raising. Such a loadingoperation/service is also called “dump approach”.

CITATIONS LIST Patent Literature

PTL 1: Japanese Patent Laying-Open No. 2008-303574

PTL 2: Japanese Patent Laying-Open No. 10-88625

SUMMARY OF INVENTION Technical Problem

In a loading operation/service, an operator needs to operate a wheelloader so as to prevent a leading end of a front wheel from collidingwith a lateral side of a dump truck and so as to prevent a workimplement (particularly, a lower end of a boom) from colliding with thelateral side of the dump truck (specifically, an upper portion of avessel). As described above, the operator needs to implement the loadingoperation/service while checking on the upper and lower locations at thesame time.

The present disclosure has been made in view of the problem describedabove. The present disclosure provides a wheel loader that assists anoperation by an operator in loading an excavated object such asexcavated soil onto a loading target (e.g., a dump truck). The presentdisclosure also provides a method for controlling the wheel loader.

Solution to Problem

According to an aspect of the present disclosure, a wheel loader forloading an excavated object onto a loading target includes: a frontframe; a bucket; a boom having a distal end connected to the bucket, anda proximal end rotatably supported by the front frame; a sensorconfigured to measure a distance between the boom and the loadingtarget; and a controller configured to control an action of the wheelloader. The controller causes the wheel loader to perform apredetermined action for collision avoidance on condition that adistance to be measured by the sensor when the wheel loader travelstakes a value less than or equal to a threshold value.

Advantageous Effects of Invention

A wheel loader according to an aspect of the present disclosure assistsan operation by an operator in loading an excavated object onto aloading target.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a wheel loader.

FIG. 2 is a top view of the wheel loader.

FIG. 3 is a perspective view of the wheel loader.

FIGS. 4(A) and 4(B) each illustrate a positional relationship between aleft boom and a sensor.

FIG. 5 schematically illustrates a sensing area of the sensor.

FIG. 6 illustrates a typical operation by an operator in dump approach.

FIGS. 7(A) and 7(B) each illustrate a situation in which the operatordoes not raise the boom to a position where an excavated object isloadable onto a vessel of a dump truck, in the dump approach.

FIG. 8 is a block diagram of a system configuration of the wheel loader.

FIG. 9 is a flowchart of a processing flow in the wheel loader.

FIG. 10 is a side view of a wheel loader.

FIG. 11 is a top view of the wheel loader.

FIG. 12 is a perspective view of the wheel loader.

FIG. 13 schematically illustrates a sensing area of a sensor.

FIG. 14 illustrates a tilt angle of a bucket.

FIG. 15 illustrates how to level off an excavated object.

DESCRIPTION OF EMBODIMENTS

Embodiments will be described below with reference to the drawings. Itis originally planned to utilize configurations of the embodiments inappropriate combination. In addition, some of constituent elements arenot employed occasionally.

A description will be given of a wheel loader with reference to thedrawings. In the following description, the terms “upper”, “lower”,“front”, “rear”, “left”, and “right” are defined with respect to anoperator who sits in an operator's seat.

A dump truck will be described as an example of a loading target ontowhich an excavated object is loaded; however, the loading target is notlimited thereto, but may be a non-self-propelled loading target such asa soil container.

First Embodiment

<Overall Configuration>

FIG. 1 is a side view of a wheel loader 1 according to a firstembodiment. FIG. 2 is a top view of wheel loader 1.

As illustrated in FIGS. 1 and 2, wheel loader 1 includes a main body 5,a work implement 30, wheels 3 a and 3 b, and an operator's cab 6. Wheelloader 1 is self-propelled in such a manner that wheels 3 a and 3 b arerotated. In addition, wheel loader 1 performs desiredoperations/services using work implement 30.

Main body 5 includes a front frame 5 a and a rear frame 5 b. Front frame5 a and rear frame 5 b are connected to each other by a center pin 81 soas to be swingable laterally.

Steering cylinders 82 are provided in a pair so as to extend from frontframe 5 a to rear frame 5 b. Each steering cylinder 82 is a hydrauliccylinder to be driven by hydraulic oil from a steering pump (notillustrated). Front frame 5 a swings relative to rear frame 5 b byexpansion and contraction of steering cylinders 82. This action changesa traveling direction of wheel loader 1.

Work implement 30 and a pair of front wheels 3 a are mounted to frontframe 5 a. Work implement 30 is disposed forward of main body 5. Workimplement 30 is driven by hydraulic oil from a hydraulic pump 119 (seeFIG. 3). Work implement 30 includes a boom 31, a pair of lift cylinders33, a bucket 32, a bell crank 34, a tilt cylinder 35, and a tilt rod 36connecting a distal end of bell crank 34 to bucket 32.

Boom 31 is rotatably supported by front frame 5 a. Boom 31 has aproximal end (proximal end) mounted to front frame 5 a by a boom pin 7such that boom 31 is swingable. Each lift cylinder 33 has a first endmounted to front frame 5 a. Each lift cylinder 33 has a second endmounted to boom 31. Preferably, the second end of each lift cylinder 33is mounted to a lower end of boom 31. Front frame 5 a and boom 31 areconnected to each other by lift cylinders 33. Boom 31 swings upward anddownward about boom pin 7 by expansion and contraction of lift cylinders33 using the hydraulic oil from hydraulic pump 119.

FIG. 1 illustrates only one of lift cylinders 33.

Bucket 32 is rotatably supported by a leading end of boom 31. Bucket 32is swingably directed to a distal end of boom 31 by a bucket pin 39.Tilt cylinder 35 has a first end mounted to front frame 5 a. Tiltcylinder 35 has a second end mounted to bell crank 34. Bell crank 34 andbucket 32 are connected to each other by a link apparatus (notillustrated). Front frame 5 a and bucket 32 are connected to each otherby tilt cylinder 35, bell crank 34, and the link apparatus. Bucket 32swings upward and downward about bucket pin 39 by expansion andcontraction of tilt cylinder 35 using the hydraulic oil from hydraulicpump 119.

Operator's cab 6 and a pair of rear wheels 3 b are mounted to rear frame5 b. Operator's cab 6 is mounted on main body 5. Operator's cab 6includes, for example, a seat in which an operator sits, and devices foroperations (to be described later).

Wheel loader 1 further includes a sensor 40 configured to measure adistance between boom 31 and a dump truck as a loading target. Sensor 40is disposed on boom 31. Sensor 40 therefore moves together with boom 31.

Specifically, sensor 40 is disposed at a predetermined position in boom31. The predetermined position is closer to the proximal end of boom 31than to the distal end of boom 31. Sensor 40 is disposed on the lowerend of boom 31. Sensor 40 is disposed near boom pin 7. As used herein,the phrase “lower end of boom 31” refers to the lower (ground side) halfof boom 31, including a lower face of boom 31.

As will be described later, sensor 40 measures a distance (hereinafter,also referred to as “distance D”) between boom 31 and a vessel of thedump truck. Sensor 40 senses the lower end of boom 31. Sensor 40 may beany device for measuring a distance. Examples of sensor 40 may includevarious devices such as an ultrasonic sensor, a laser sensor, aninfrared sensor, and a camera.

FIG. 3 is a perspective view of wheel loader 1. As illustrated in FIG.3, boom 31 is raised based on an operation by the operator, so thatbucket 32 is also raised. The operator decreases a tilt angle (angle θin FIG. 14) of bucket 32 with an excavated object such as excavated soilloaded on the bucket. The excavated object is thus loaded onto theloading target such as the dump truck.

FIGS. 4(A) and 4(B) each illustrate a positional relationship betweenleft boom 31 and sensor 40. As illustrated in FIGS. 4(A) and 4(B),sensor 40 is disposed on lower end 31 a of boom 31. Sensor 40 includes ahousing, and a lens 41 disposed in the housing at a position near thedistal end of boom 31.

In wheel loader 1, lens 41 is disposed on the right side of left boom 31(i.e., is disposed on left boom 31 at a position near right boom 31);however, the present disclosure is not limited to this configuration.For example, lens 41 may be disposed on the left side of left boom 31.Alternatively, the sensor may be disposed on right boom 31.

FIG. 5 schematically illustrates a sensing area of sensor 40. Asillustrated in FIG. 5, sensor 40 is disposed such that an optical axis48 of sensor 40 extends along boom 31.

Sensor 40 senses an area covering lower end 31 a of boom 31. Sensor 40may sense an area closer to the distal end of boom 31 than to theproximal end of boom 31, in lower end 31 a of boom 31. Preferably,sensor 40 senses an area ranging from the position of the second end ofeach lift cylinder 33 mounted to boom 31 to the distal end of boom 31,in lower end 31 a of boom 31. Alternatively, sensor 40 may sense a partof each area described above.

Sensor 40 disposed as described above measures a distance between boom31 and the dump truck as the loading target. Information acquired bysensor 40 is sent to a controller 110 (FIG. 8) of wheel loader 1 andthen is subjected to data processing in controller 110 as will bedescribed later.

<Dump Approach>

FIG. 6 illustrates a typical operation by the operator in dump approach.As illustrated in FIG. 6, the operator initiates acceleration in asection Q11. Specifically, the operator presses an accelerator pedal(not illustrated). Also in section Q11, the operator actuates a boomcontrol lever 122 (FIG. 8) to raise boom 31 as will be described later.In section Q11, wheel loader 1 thus travels toward dump truck 900 whileperforming boom-raising.

The operator initiates acceleration in section Q11 for the purpose ofsupplying a satisfactory amount of oil to lift cylinders 33, rather thanfor the purpose of causing wheel loader 1 to travel. Increasing anengine speed ensures an output of hydraulic oil from the hydraulic pump.Accordingly, the operator still presses the accelerator pedal even whenhe or she presses a brake pedal to decrease a vehicle speed in sectionQ11.

In a section Q12 subsequent to section Q11, the operator ceases theacceleration and then initiates braking. Specifically, the operatorpresses the brake pedal (not illustrated) instead of the acceleratorpedal. The operator thus brings wheel loader 1 to a stop in front ofdump truck 900. Thereafter, the operator actuates a bucket control lever123 (FIG. 8) to load soil scooped by bucket 32 onto a bed of dump truck900 as will be described later.

A broken line La represents a path along which bucket 32 typically movesin the series of operations.

FIGS. 7(A) and 7(B) each illustrate a situation in which the operatordoes not raise boom 31 to a position where an excavated object isloadable onto vessel 901 of dump truck 900, in the dump approach. FIG.7(A) illustrates the dump approach on the assumption that an output fromsensor 40 is not utilized. FIG. 7(B) illustrates the dump approach onthe assumption that an output from sensor 40 is utilized. FIG. 7(A)illustrates a comparative example for clarifying a feature of the dampapproach in FIG. 7(B).

As illustrated in FIG. 7(A), if the operator does not raise boom 31 to aheight illustrated in FIG. 6 in section Q11, the following event canoccur in section Q12. In order to avoid a leading end of each frontwheel 3 a in wheel loader 1 from colliding with a lateral side of dumptruck 900, the operator causes wheel loader 1 to travel forward whileseeing front wheels 3 a. As a result, the lower end of boom 31 collideswith an upper portion of vessel 901 of dump truck 900 before each frontwheel 3 a arrives at a position where the operator intends to stop wheelloader 1. According to this embodiment, the use of sensor 40 enablesavoidance of this event. With reference to FIG. 7(B), a description willbe given of how to avoid this event. In FIG. 7(A), a broken line Lbrepresents a path of bucket 32.

If the operator does not raise boom 31 to the height illustrated in FIG.6 in section Q11, wheel loader 1 (specifically, controller 110) controlsboom-raising as illustrated in FIG. 7(B).

Wheel loader 1 determines whether distance D to be measured by sensor 40(i.e., the distance between boom 31 and dump truck 900) takes a valueless than or equal to a threshold value. When wheel loader 1 determinesthat the value of distance D measured is less than or equal to thethreshold value, then wheel loader 1 starts to raise boom 31. Forexample, wheel loader 1 does not raise boom 31 in a section Q21 duringwhich the value of distance D measured is larger than the thresholdvalue. When wheel loader 1 arrives at a section Q22 during which thevalue of distance D measured is less than or equal to the thresholdvalue, then wheel loader 1 starts to raise boom 31.

As described above, wheel loader 1 includes sensor 40 configured tomeasure distance D between boom 31 and dump truck 900. Controller 110 ofwheel loader 1 causes wheel loader 1 to perform boom-raising oncondition that distance D to be measured by sensor 40 when wheel loader1 travels takes a value less than or equal to the threshold value.

As described above, wheel loader 1 moves boom 31 away from vessel 901before collision of boom 31 with vessel 901 in the dump approach. Wheelloader 1 accordingly avoids the collision of boom 31 with dump truck 900even when the operator neglects to confirm the position of boom 31because he or she pays excessive attention to the position of each frontwheel 3 a. Wheel loader 1 therefore assists the operation by theoperator in the dump approach.

<Functional Configuration>

FIG. 8 is a block diagram of a system configuration of wheel loader 1.As illustrated in FIG. 8, wheel loader 1 includes boom 31, bucket 32,lift cylinders 33, tilt cylinder 35, sensor 40, controller 110, a boomangle sensor 112, a bucket angle sensor 113, an engine 118, hydraulicpump 119, a control lever 120, control valves 131 and 141, a monitor151, and a speaker 152.

Control lever 120 includes a fore/aft traveling switch control lever121, boom control lever 122, bucket control lever 123, and vibrators124, 125, and 126. Controller 110 includes a determination unit 1101.

Controller 110 controls the overall actions of wheel loader 1.Controller 110 controls, for example, a rotation speed of engine 118,based on the actuation of the accelerator pedal. In addition, thecontroller receives a signal based on the actuation of control lever 120by the operator, and then causes wheel loader 1 to perform an action inaccordance with the actuation.

Hydraulic pump 119 is driven by an output from engine 118. Hydraulicpump 119 supplies the hydraulic oil to lift cylinders 33 via controlvalve 131 such that boom 31 is driven. Boom 31 is raised or lowered byactuation of boom control lever 122 in operator's cab 6. Hydraulic pump119 also supplies the hydraulic oil to tilt cylinder 35 via controlvalve 141 such that bucket 32 is driven. Bucket 32 is acted by actuationof bucket control lever 123 in operator's cab 6.

Controller 110 successively receives results of sensing from sensor 40.In the dump approach, determination unit 1101 of controller 110determines whether distance D to be measured by sensor 40 takes a valueless than or equal to threshold value Th. When determination unit 1101determines that the value of distance D is less than or equal tothreshold value Th, controller 110 starts to raise boom 31.

Controller 110 receives a signal according to a boom angle from boomangle sensor 112. Controller 110 also receives a signal according to atilt angle from bucket angle sensor 113. A description will be given ofhow to utilize signals (results of sensing) output from boom anglesensor 112 and bucket angle sensor 113, later.

Controller 110 causes monitor 151 to display various images. Controller110 causes speaker 152 to output a predetermined sound. A descriptionwill be given of how to utilize monitor 151 and speaker 152, later.

Vibrator 124 is configured to vibrate fore/aft traveling switch controllever 121. Vibrator 125 is configured to vibrate boom control lever 122.Vibrator 126 is configured to vibrate bucket control lever 123. Adescription will be given of how to utilize vibrators 124 to 126, later.

<Control Structure>

FIG. 9 is a flowchart of a processing flow in wheel loader 1. Asillustrated in FIG. 9, in step S2, controller 110 determines whetherwheel loader 1 is traveling forward. When controller 110 determines thatwheel loader 1 is traveling forward (YES in step S2), then, in step S4,controller 110 determines whether distance D measured by sensor 40 takesa value less than or equal to threshold value Th. When controller 110determines that wheel loader 1 is not traveling forward (NO in step S2),the processing goes back to step S2.

When controller 110 determines that the value of distance D is less thanor equal to threshold value Th (YES in step S4), then, in step S6,controller 110 starts to raise boom 31. When controller 110 determinesthat the value of distance D is larger than threshold value Th (NO instep S4), the processing goes back to step S2. In step S8, controller110 determines whether distance D measured by sensor 40 takes a valueless than or equal to threshold value Th.

When controller 110 determines that the value of distance D is largerthan threshold value Th (YES in step S8), then, in step S14, controller110 stops boom 31 being raised. In step S16 subsequent to step S14,controller 110 determines whether wheel loader 1 is traveling forward.When controller 110 determines that wheel loader 1 is traveling forward(YES in step S16), the processing goes back to step S4. When controller110 determines that wheel loader 1 is not traveling forward (NO in stepS16), the processing ends.

When controller 110 determines that the value of distance D is less thanor equal to threshold value Th (NO in step S8), then, in step S10,controller 110 determines whether an angle (a boom angle) of boom 31 ismaximum. Specifically, controller 110 determines whether each of liftcylinders 33 has extended to its stroke end.

When controller 110 determines that the boom angle is maximum (YES instep S10), then, in step S12, controller 110 brings wheel loader 1 to astop. Typically, controller 110 initiates braking even when the operatordoes not press the braking pedal. When controller 110 determines thatthe boom angle is not maximum (NO in step S10), the processing goes tostep S8.

As described above, controller 110 causes wheel loader 1 to raise boom31 on condition that distance D takes a value less than or equal tothreshold value Th. Wheel loader 1 may be configured to allow theoperator to forcibly cease the control by controller 110. Examples ofsuch an operation by the operator may include an operation to press downa predetermined button (not illustrated), an operation to actuate boomcontrol lever 122 to lower boom 31, and an operation to shift fore/afttraveling switch control lever 121 from a fore traveling position to anaft traveling position. In wheel loader 1, the operator performs theoperation to shift fore/aft traveling switch control lever 121 from thefore traveling position to the aft traveling position even when wheelloader 1 is traveling forward (i.e., is not stopping).

Advantages

(1) As described above, sensor 40 is disposed at the predeterminedposition in boom 31. The predetermined position is closer to theproximal end of boom 31 than to the distal end of boom 31. Controller110 causes wheel loader 1 to perform the predetermined action forcollision avoidance, that is, the action to raise boom 31 on conditionthat distance D to be measured by sensor 40 when wheel loader 1 travelstakes a value less than or equal to threshold value Th.

With this configuration, wheel loader 1 moves boom 31 away from vessel901 as shown with section Q22 in FIG. 7(B) before collision of boom 31with vessel 901 in the dump approach. Wheel loader 1 therefore avoidsthe collision of boom 31 with dump truck 900 even when the operatorneglects to confirm the position of boom 31. Wheel loader 1 thus assiststhe operation by the operator in the dump approach.

(2) Specifically, the predetermined position corresponds to lower end 31a of boom 31. This configuration enables sensing on lower end 31 a ofboom 31.

(3) Sensor 40 senses lower end 31 a of boom 31. This configurationenables measurement of distance D between boom 31 and vessel 901 of dumptruck 900.

(4) Controller 110 brings wheel loader 1 to a stop on condition that theangle of boom 31 is maximum. This configuration prevents collision ofboom 31 with vessel 901 in a situation in which boom 31 collides withvessel 901 even when boom 31 is retreated as much as possible.

Second Embodiment

A description will be given of a wheel loader according to a secondembodiment with reference to the drawings. It should be noted that adescription will be given of different configurations of the wheelloader according to the second embodiment from those of wheel loader 1according to the first embodiment; therefore, no description will begiven of similar configurations of the wheel loader according to thesecond embodiment to those of wheel loader 1 according to the firstembodiment.

FIG. 10 is a side view of wheel loader 1A according to the secondembodiment. FIG. 11 is a top view of wheel loader 1A. FIG. 12 is aperspective view of wheel loader 1A.

As illustrated in FIGS. 10, 11, and 12, wheel loader 1A has a hardwareconfiguration similar to the hardware configuration of wheel loader 1A,except for a sensor 40A provided instead of sensor 40.

Sensor 40A is disposed on an upper face of a front frame 5 a. Sensor 40Ais disposed at a predetermined position that is closer to a positionwhere a boom 31 is supported than to a front end 51 (see FIG. 13) offront frame 5 a. Specifically, sensor 40A is disposed closer to a boompin 7 than to the front end of front frame 5 a.

Sensor 40A is disposed between a position where left boom 31 issupported and a position where a tilt cylinder 35 is supported, as seenin top view in a Y direction illustrated in FIG. 11. Sensor 40A may bedisposed between a position where right boom 31 is supported and theposition where tilt cylinder 35 is supported, as seen in top view.

Sensor 40A measures a distance D between boom 31 and dump truck 900 indump approach, as in a manner similar to that of sensor 40.Specifically, sensor 40A measures distance D between boom 31 and vessel901 of dump truck 900, as in a manner similar to that of sensor 40.Sensor 40A senses a lower end of boom 31 with boom 31 raised, as in amanner similar to that of sensor 40. Sensor 40A may be any device formeasuring distance D. Examples of sensor 40A may include various devicessuch as an ultrasonic sensor, a laser sensor, an infrared sensor, and acamera.

FIG. 13 schematically illustrates a sensing area of sensor 40A. Asillustrated in FIG. 13, sensor 40A is disposed such that an optical axis49 of sensor 40A approximately extends along boom 31 with boom 31 raisedat an angle greater than or equal to a predetermined angle. The sensingarea of sensor 40A is set in advance with a boom angle in the dumpapproach taken into consideration.

Sensor 40A senses an area covering a lower end 31 a of boom 31. Sensor40A may sense an area closer to a distal end of boom 31 than to aproximal end of boom 31, in lower end 31 a of boom 31. Preferably,sensor 40A senses an area ranging from a position of a second end ofeach lift cylinder 33 mounted to boom 31 to the distal end of boom 31,in lower end 31 a of boom 31. Alternatively, sensor 40A may sense a partof each area described above.

Sensor 40A disposed as described above measures distance D between boom31 and the dump truck as the loading target. Information acquired bysensor 40A is sent to a controller 110 of wheel loader 1A and then issubjected to data processing in controller 110.

Controller 110 of wheel loader 1A operates like controller 110 of wheelloader 1. Specifically, controller 110 causes wheel loader 1 to performa predetermined action for collision avoidance, that is, an action toraise boom 31 on condition that distance D to be measured by sensor 40Awhen wheel loader 1A travels takes a value less than or equal to athreshold value Th.

With this configuration, wheel loader 1A moves boom 31 away from vessel901 before collision of boom 31 with vessel 901 in the dump approach.Wheel loader 1A therefore avoids the collision of boom 31 with dumptruck 900 even when the operator neglects to confirm the position ofboom 31 because he or she operates wheel loader 1A while directing hisor her line of sight to front wheels 3 a.

Modifications

A description will be given of a modification of wheel loader 1according to the first embodiment and a modification of wheel loader 1Aaccording to the second embodiment with reference to the drawings.

(1) Predetermined Action for Collision Avoidance

In the first and second embodiments, controller 110 causes wheel loader1 to perform the predetermined action, that is, the action to raise boom31 on condition that distance D to be measured by sensor 40A when wheelloader 1A travels takes a value less than or equal to threshold valueTh. However, the predetermined action is not limited to the action toraise boom 31.

Controller 110 may cause speaker 152 to output a predetermined audiblenotification (audible alarm), in place of the control for raising boom31. Alternatively, controller 110 may cause monitor 151 to display apredetermined warning. These configurations each make the operator awareof an abnormal state. Specifically, the operator is able to recognizethat wheel loader 1, 1A almost collides with the dump truck.

Controller 110 may send a command to each of vibrators 124 to 126 suchthat vibrators 124 to 126 start to vibrate. The vibrations of vibrators124, 125, and 126 vibrate corresponding control levers 121, 122, and123. This configuration also makes the operator aware of an abnormalstate.

Wheel loader 1, 1A may be configured to perform the action to raise boom31, the output of the predetermined audible alarm from speaker 152, thedisplay of the predetermined warning on monitor 151, and the vibrationsof vibrators 124 to 126 in appropriate combination.

(2) Control with Tilt Angle Taken into Consideration

FIG. 14 illustrates a tilt angle θ of bucket 32. It should be noted thatFIG. 14 illustrates wheel loader 1. As illustrated in FIG. 14, since anexcavated object such as soil is loaded on bucket 32 in the dumpapproach, the operator needs to set tilt angle θ to be larger than apredetermined angle (hereinafter, also referred to as “angle θ1”).

Therefore, wheel loader 1, 1A is not configured to always perform thepredetermined action on condition that distance D takes a value lessthan or equal to threshold value Th, but may be configured to performthe predetermined action on condition that the tilt angle of bucket 32is greater than or equal to predetermined angle θ1.

With this configuration, in a situation in which wheel loader 1, 1Aapproaches dump truck 900 with an excavated object loaded on bucket 32,wheel loader 1, 1A performs the predetermined action on condition thatdistance D takes a value less than or equal to threshold value Th. Onthe other hand, in a situation in which wheel loader 1, 1A approachesdump truck 900 with no excavated object loaded on bucket 32, wheelloader 1, 1A does not perform the predetermined action on condition thatthe value of distance D is less than or equal to threshold value Th.

As described above, wheel loader 1, 1A approaching dump truck 900 doesnot perform the predetermined action on condition that no excavatedobject is loaded on bucket 32.

FIG. 15 illustrates how to level off an excavated object. It should benoted that FIG. 15 illustrates wheel loader 1. As illustrated in FIG.15, when the operator operates wheel loader 1 to load an excavatedobject onto vessel 901 of dump truck 900, the excavated object can beheaped on vessel 901 beyond the height of vessel 901. In such a case,the operator sets the tilt angle of bucket 32 to be less than or equalto a predetermined angle (hereinafter, referred to as “angle θ2”) thatis smaller than angle 81. The operator then operates bucket 32 to dropthe excavated object heaped beyond the upper side of vessel 901.Typically, tilt angle θ of bucket 32 is set at zero (i.e., a state inwhich a cutting edge 32 a is horizontal to main body 5), and then thesoil heaped beyond the upper side of vessel 901 is dropped onto theground opposite from wheel loader 1, 1A across dump truck 900.

The operator fails to level off the excavated object if boom 31 isautomatically raised since the value of distance D is less than or equalto threshold value Th. Hence, controller 110 causes wheel loader 1 tostop the predetermined action, that is, boom-raising on condition thattilt angle θ is less than or equal to angle θ2 that is smaller thanangle θ1. This configuration allows the operator to level off theexcavated object.

(3) Stop of Control in Aft Traveling

In aft traveling of wheel loader 1, 1A, boom 31 never collides withvessel 901 even when the value of distance D is less than or equal tothreshold value Th. Wheel loader 1, 1A therefore has no necessity toperform the predetermined action such as the action to raise boom 31.Hence, controller 110 may be configured to cause wheel loader 1, 1A tostop the predetermined action after a transition of wheel loader 1, 1Afrom a fore traveling state to an aft traveling state. Thisconfiguration avoids execution of unnecessary control.

<<Additional Remarks>>

A wheel loader for loading an excavated object onto a loading targetincludes: a front frame; a bucket; a boom having a distal end connectedto the bucket, and a proximal end rotatably supported by the frontframe; a sensor configured to measure a distance between the boom andthe loading target; and a controller configured to control an action ofthe wheel loader. The controller causes the wheel loader to perform apredetermined action for collision avoidance on condition that adistance to be measured by the sensor when the wheel loader travelstakes a value less than or equal to a threshold value.

With this configuration, the wheel loader traveling forward performs thepredetermined action for collision avoidance before collision of theboom with the loading target. The wheel loader therefore avoids thecollision of the boom with the loading target even when an operatorneglects to confirm a position of the boom. The wheel loader thusassists an operation by the operator in loading the excavated objectonto the loading target.

Preferably, the sensor is disposed at one of a first position in theboom, the first position being closer to the proximal end of the boomthan to the distal end of the boom, and a second position in the frontframe, the second position being closer to a position where the boom issupported than to a front end of the front frame. Also preferably, thefirst position corresponds to a lower end of the boom.

This configuration allows the sensor of the wheel loader to sense thelower end of the boom.

Preferably, the sensor is disposed at the first position and isconfigured to sense an area covering a lower end of the boom, the areabeing closer to the distal end of the boom than to the proximal end ofthe boom.

This configuration allows the wheel loader to measure the distancebetween the boom and the loading target.

Preferably, the wheel loader further includes a lift cylinder having oneend mounted to a lower end of the boom, the lift cylinder beingconfigured to drive the boom. The sensor is disposed at the firstposition and is configured to sense an area ranging from a position ofthe lift cylinder mounted to the boom to the distal end of the boom, inthe lower end of the boom.

This configuration allows the wheel loader to measure the distancebetween the boom and the loading target.

Preferably, the predetermined action corresponds to an action to raisethe boom.

This configuration allows the wheel loader traveling forward to move theboom away from the loading target before collision of the boom with theloading target. This configuration therefore allows the wheel loader toavoid the collision of the boom with the loading target even when theoperator neglects to confirm the position of the boom.

Preferably, the predetermined action corresponds to an action to outputa predetermined audible notification.

This configuration allows the operator to perform an operation to avoidcollision of the boom with the loading target in such a manner that theoperator listens to the audible notification before the collision of theboom with the loading target.

Preferably, the wheel loader further includes a control lever configuredto operate the wheel loader. The predetermined action corresponds to anaction to vibrate the control lever.

This configuration allows the operator to perform the operation to avoidcollision of the boom with the loading target in such a manner that theoperator feels the vibration of the control lever before the collisionof the boom with the loading target.

Preferably, the controller brings the wheel loader to a stop oncondition that the boom is raised at a maximum angle by thepredetermined action.

This configuration prevents collision of the boom with the loadingtarget in a situation in which the boom collides with the loading targeteven when the boom is retreated as much as possible.

Preferably, the controller causes the wheel loader to perform thepredetermined action on condition that a tilt angle of the bucket takesa value greater than or equal to a first value.

This configuration prevents the wheel loader approaching the loadingtarget from performing the predetermined action for collision avoidanceon condition that no excavated object is loaded on the bucket.

Preferably, the predetermined action corresponds to an action to raisethe boom. The controller causes the wheel loader to stop the action toraise the boom on condition that the tilt angle takes a value less thanor equal to a second value that is smaller than the first value.

With this configuration, the operator levels off the excavated objectsince the wheel loader stops automatic control for boom-raising.

Preferably, the controller causes the wheel loader to stop thepredetermined action on condition that the controller receives apredetermined input based on an operation by the operator.

With this configuration, the operator forcibly stops the control forraising the boom on condition that the distance between the boom and theloading target takes a value less than or equal to the threshold value.

Preferably, the predetermined action corresponds to an action to raisethe boom. The operation by the operator corresponds to an operation tolower the boom.

With this configuration, the operator performs the operation to lowerthe boom when the boom is automatically raised. This operation enables aforcible stop of the control for automatically raising the boom.

Preferably, the wheel loader further includes a fore/aft travelingswitch lever configured to switch between fore traveling of the wheelloader and aft traveling of the wheel loader. The operation by theoperator corresponds to an operation to shift the fore/aft travelingswitch lever from a fore traveling position to an aft travelingposition.

With this configuration, the fore/aft traveling switch lever switchingoperation allows a forcible stop of the control for raising the boom oncondition that the distance between the boom and the loading targettakes a value less than or equal to the threshold value.

Preferably, the controller causes the wheel loader to stop thepredetermined action after a transition of the wheel loader from a foretraveling state to an aft traveling state.

With this configuration, the controller causes the wheel loader in theaft traveling state to stop the action to raise the boom on conditionthat the distance between the boom and the loading target takes a valueless than or equal to the threshold value.

A method for controlling a wheel loader configured to load an excavatedobject onto a loading target includes the steps of: measuring a distancebetween a boom of the wheel loader and the loading target; determiningthat the distance measured takes a value less than or equal to athreshold value when the wheel loader travels; and causing the wheelloader to perform a predetermined action for collision avoidance oncondition that the value of the distance measured is less than or equalto the threshold value.

By this method, the wheel loader traveling forward performs thepredetermined action for collision avoidance before collision of theboom with the loading target. The wheel loader therefore avoids thecollision of the boom with the loading target even when the operatorneglects to confirm the position of the boom. The wheel loader thusassists an operation by the operator in loading the excavated objectonto the loading target.

It should be understood that the embodiments disclosed herein are in allaspects illustrative and not restrictive. The scope of the presentinvention is defined by the appended claims rather than the foregoingdescription, and all changes that fall within metes and bounds of theclaims, or equivalence such metes and bounds thereof are thereforeintended to be embraced by the claims.

REFERENCE SIGNS LIST

1, 1A: wheel loader, 3 a: front wheel, 3 b: rear wheel, 5: main body, 5a: front frame, 5 b: rear frame, 6: operator's cab, 7: boom pin, 30:work implement, 31: boom, 31 a: lower end, 32: bucket, 32 a: cuttingedge, 33: lift cylinder, 34: bell crank, 35: tilt cylinder, 36: tiltrod, 39: bucket pin, 40, 40A: sensor, 41: lens, 48, 49: optical axis,900: dump truck, 901: vessel

The invention claimed is:
 1. A wheel loader comprising: a front frame; abucket; a boom having a distal end connected to the bucket, and aproximal end rotatably supported by the front frame; a sensor configuredto measure a distance between the boom and a loading target, wherein anexcavated object is configured to be loaded by the wheel loader onto theloading target; and a controller configured to control an action of thewheel loader, wherein the controller causes the wheel loader, when thewheel loader is travelling, to perform a predetermined action forcollision avoidance based on the distance measured by the sensor beingless than or equal to a threshold value.
 2. The wheel loader accordingto claim 1, wherein the sensor is disposed at one of a first position onthe boom, the first position being closer to the proximal end of theboom than to the distal end of the boom, and a second position in thefront frame, the second position being closer to a position where theboom is supported than to a front end of the front frame.
 3. The wheelloader according to claim 2, wherein the sensor is disposed at the firstposition on the boom, and the first position corresponds to a lower endof the boom.
 4. The wheel loader according to claim 2, wherein thesensor is disposed at the first position on the boom and is configuredto sense an area covering a lower end of the boom, the area being closerto the distal end of the boom than to the proximal end of the boom. 5.The wheel loader according to claim 2, further comprising: a liftcylinder having one end mounted to a lower end of the boom, the liftcylinder being configured to drive the boom, wherein the sensor isdisposed at the first position on the boom and is configured to sense anarea ranging from a position of the lift cylinder mounted to the boom tothe distal end of the boom, in the lower end of the boom.
 6. The wheelloader according to claim 1, wherein the predetermined actioncorresponds to an action to raise the boom.
 7. The wheel loaderaccording to claim 1, wherein the predetermined action corresponds to anaction to output a predetermined audible notification.
 8. The wheelloader according to claim 1, further comprising: a control leverconfigured to operate the wheel loader, wherein the predetermined actioncorresponds to an action to vibrate the control lever.
 9. The wheelloader according to claim 6, wherein the controller brings the wheelloader to a stop on condition that the boom is raised at a maximum angleby the predetermined action.
 10. The wheel loader according to claim 1,wherein the controller causes the wheel loader to perform thepredetermined action on condition that a tilt angle of the bucket takesa value greater than or equal to a first value.
 11. The wheel loaderaccording to claim 10, wherein the predetermined action corresponds toan action to raise the boom, and the controller causes the wheel loaderto stop the action to raise the boom on condition that the tilt angletakes a value less than or equal to a second value that is smaller thanthe first value.
 12. The wheel loader according claim 1, wherein thecontroller causes the wheel loader to stop the predetermined action oncondition that the controller receives a predetermined input based on anoperation by the operator.
 13. The wheel loader according to claim 12,wherein the predetermined action corresponds to an action to raise theboom, and the operation by the operator corresponds to an operation tolower the boom.
 14. The wheel loader according to claim 12, furthercomprising: a fore/aft traveling switch lever configured to switchbetween fore traveling of the wheel loader and aft traveling of thewheel loader, wherein the operation by the operator corresponds to anoperation to shift the fore/aft traveling switch lever from a foretraveling position to an aft traveling position.
 15. The wheel loaderaccording claim 1, wherein the controller causes the wheel loader tostop the predetermined action after a transition of the wheel loaderfrom a fore traveling state to an aft traveling state.
 16. A method forcontrolling a wheel loader, comprising the step of: measuring a distancebetween a boom of the wheel loader and a loading target, wherein anexcavated object is configured to be loaded by the wheel loader onto theloading target; determining, when the wheel loader is travelling,whether the measured distance is less than or equal to a thresholdvalue; and causing the wheel loader to perform a predetermined actionfor collision avoidance based on the measured distance being less thanor equal to the threshold value.
 17. The wheel loader according claim 1,wherein the controller causes the wheel loader, when the wheel loader istravelling forward, to perform the predetermined action for collisionavoidance based on the distance measured by the sensor being less thanor equal to a threshold value.